The invention concerns a device for independent actuation of the phase and axial position of a camshaft.
Otto motors usually operate with a load-dependent change of the fuel-air mixture. This is, as a rule, varied by a throttling device, for example by a throttle valve. This leads to throttling losses during load changes. The throttling losses can be diminished by variation of the aperture cross section of the intake valves, for example by changing its stroke. For this, for example, an axially moveable intake camshaft with a conical or three-dimensional cam contour is suitable.
A strong charging movement is also advantageous with a partial load as it can be triggered by a retarded beginning of suction. The high rate of combustion caused by this also brings about, even with retarded beginning of suction, a punctual end of combustion. A retarded beginning of combustion with a punctual end of combustion however brings about a low peak pressure, a slight tendency to knock and low nitrogen oxide formation without several combustion disadvantages. The shifting of opening and closing times of the intake and if need be the exhaust valves required for this can be realized by known phase adjusters arranged in the power train between crankshaft and camshaft. Variable valve cross sections and control times are accordingly advantageous for an economical and environmentally friendly operation of the Otto motor.
From DE 199 02 095 A, a device for independent hydraulic actuation of the phase and axial position of a camshaft is known. For reasons of construction space, the phase adjuster is arranged on the directly driven exhaust camshaft. Its output element is connected with a gear which is mounted on the exhaust camshaft and which drives the gear of the intake camshaft. The motor-attached stroke actuator is connected with this through a slide gearing. The slide gearing must be provided with minimal backlash as this is a source of disturbing noises. The same applies for the tooth wheel drive between the two camshafts. For this reason, with this solution, an expensive compensation for or restriction of the torsional backlash is provided.
From DE 199 03 622 A1, a device for independent hydraulic actuation of the phase and axial position of a shaft, especially the intake camshaft of an internal combustion engine, is known, with a phase adjuster constructed as rotatble piston actuator, which has a stator and a rotor, and with an actuating piston arranged in the same axis for axial movement of the intake camshaft. In addition, this device has a cylindrical housing for the actuating piston whereby the housing is connected with the stator and a drive wheel and the rotor as well as the actuating piston are in a rotationally fixed connection with the intake camshaft.
Since the actuators are arranged one after the other, they require a considerable construction length. Since the phase adjuster is positioned axially stationary, they require, in relation to the axially movable camshaft, a sliding gearing with the known expensive measures for avoiding gear backlash.
Underlying the invention is the object of creating a generic device for independent hydraulic actuation of the phase and axial position of a camshaft whereby the device is distinguished by a small space requirement and low construction expenditure.
In accordance with the invention, this object is accomplished by providing a device in which the phase adjuster also forms the actuating piston for the camshaft. Since the phase adjuster is at the same time the actuating piston of the camshaft, it moves along with the axial movement of the camshaft. In this way, the necessity of a slide gearing in addition to gear backlash compensation between phase adjuster and camshaft is dispensed with, which leads to a considerable simplification of the device. Dispensing with a separate actuation piston likewise diminishes construction expense and at the same time diminishes the overall length of the device.
A preferred embodiment of the invention is provided in that the phase adjuster is constructed as a segment vane actuator which has a cylindrical rotor, in the peripheral area of which at least one axial, concentric hydraulic chamber in the form of a oblong hole is provided. The hydraulic chamber is subdivided by a segment into two active oil chambers A and B with sealing play and is laterally closed off by two side covers with close play. Here the side covers have apertures aligning with the cross section shape of the segment through which the same extends with sealing play. Such a segment vane actuator is described in the not previously published German patent application P 199 51 390.2. It is distinguished by a small number of structural units and its economical producibility. While the segments described in the not previously published German patent application P 199 51 390.2 are inserted between the side covers, these extend, in the construction of the invention, through the aligning apertures of the side covers. These aligning apertures permit a lengthening of the segments over the width of the rotor so that these can serve as guide rods during axial motion of the segment vane actuator. The close play between the apertures and the segments moreover serve for lateral sealing of the active oil chambers A and B.
An advantageous refinement of the invention is provided in that the length of the segments exceeds the greatest width of the rotor at least by the stroke dimension of the camshaft, and in that the constructed hollow segments are clamped from rotating by means of bolts that extend through the same between a bottom of the housing and a cover plate preferably constructed as a drive wheel. The length of the segments selected permits the desired axial displacement of the segment vane actuator and the intake camshaft connected with it. The driving torque of the camshaft is transferred from the drive wheel through the segments inserted between this and the housing and the pressure oil in active oil chambers A and B to the rotor and the camshaft connected with it.
It is advantageous if the rotor has, on both sides, coaxial, cylindrical recesses for the side covers and that the side covers are axially fixed though retaining rings. Since the side covers, in the construction of the segment vane actuator of the invention, cannot be braced on one another, their close play in relation to the rotor is guaranteed through the exact axial position of the retaining rings sitting in the grooves of the same. The side walls moreover serve exclusively for lateral sealing of active oil chambers A and B and not for transfer of the driving torque of the segments.
An appropriate construction of the invention is provided in that on the periphery of the rotor, at least sealing element is arranged though which the cylindrical housing is subdivided into first and second operating chambers. Since the rotor is radially guided by the segments, it must have radial play in relation to the cylindrical housing which is bridged by the sealing element. The sealing element can be constructed as a sealing ring, sealing strip or piston guide way.
Due to the fact that first and second 4/3 way proportional valve are provided for independent hydraulic control of active oil chambers A and B and the first and second chambers, a motor-optimal control of the camshafts is made possible.
It is advantageous that a preferably decentralized control apparatus is provided for the proportional valves which receives signals on phase and stroke position of the camshaft from a camshaft sensor and such on, for example, motor speed, motor load and motor temperature from a central control apparatus of the internal combustion engine. The central control apparatus makes possible a flexible supplementation of the motor control apparatus which is not affected by possible changes of the camshaft.
Preferably a seal ring carrier of a rotary oil through passage device is located between rotor and intake camshaft, which has oil sealing rings for mutual and outward acting sealing of the radial grooves of oil supply channels. In this way, oil leakage losses of the rotary oil through passage with a relatively long overall length are minimized.
An advantageous refinement of the invention is provided in that the radial forces of the drive wheel are transmissible over the segments and the rotor or directly to the sealing ring carrier and the camshaft. The mounting of the drive wheel over the segments on the walls of the hydraulic chambers (the so-called internal mounting) offers the advantage of the smallest play possible between active oil chambers A and B with correspondingly low leakage. A precondition for this is a correspondingly wear and tear resistant surface of the walls of the hydraulic chambers. In contrast, with direct mounting of the driving wheel on the seal ring carrier (or so-called external mounting), owing to the bearing play there, a corresponding enlargement of the close play of the segments in the hydraulic chambers is necessary, which has increased oil leakage losses or the installation of additional sealing elements as a consequence. For this, the walls of the hydraulic chambers in this case require no protection against wear and tear, so that the rotor can be formed of light metal, for example, of aluminum, and be manufactured by the extrusion or cold forging method.
Due to the fact that the rotor has a locking element, preferably an axial fixing pin which is latchable in a blind aperture of one of the side covers, the starting position of the rotor is assured which among other things is important for a good motor start. Of course, the use of a radial fixation pin or a wedge locking device or the like is also conceivable.
Further features of the invention are provided in the patent claims, the following description and the drawings in which an embodiment of the invention is schematically represented.